Many types of materials have been developed to restore tooth. Although the use of amalgam has been common in dentistry, over the last few decades the tooth-colored restorative materials have become more popular. These compositions generally comprise polymerizable ethylenically unsaturated monomers and an inert filler. The resin systems generally consist of mixtures of Bis-GMA, TEGDMA, Urethane dimethacrylates etc. The resultant restorative compositions are generally quite hydrophobic and immiscible with water, and hence require the elimination of water from the surface of the tooth structure to be restored. The clinical procedure calls for stringent moisture control through the use of rubber dam or other suitable procedure. However, since moisture is constantly replenished in the mouth through saliva flow and/or exudation of dentinal fluid, its control makes the restorative procedure quite challenging for the practitioner. Hydrophilic compositions, on the other hand, can imbibe water from the surrounding environment. Water-based cement compositions, particularly the glass ionomer cements, are tolerant of extraneous moisture. Thus the cements described by Wilson et al. have been used advantageously. These are two part powder:liquid systems consisting of a solution of a polyalkenoic acid in water and an acid-reactive glass powder. Modifications of these cements by incorporation of curable moieties to obtain in situ polymerizable cements have been described. A particularly attractive benefit of these cements is the prolonged release of high amounts of fluoride from the set cements in the oral environment. It is believed that this leads to a protection from secondary caries attack. The disadvantage of these cements, however, is that they are generally two-part powder:liquid systems and require mixing prior to use. Furthermore, the glass ionomer cement materials in general have much lower mechanical properties compared to the resin-based composites. Hence their use is confined to non-stress bearing applications. In order to overcome this disadvantage, other systems have been devised, such as described in U.S. Pat. No. 5,151,453. The fluoride release levels from these materials, however, is quite low compared to the glass ionomer cements.
Additionally, having good handling properties in restorative filling materials is so important to the dentist, it is not surprising that there are numerous citations in the literature claiming materials with such properties. See e.g. DE 4447275; JP 56120610; JP 03077804; JP 06065022; JP 07061904; JP 08119820; EP 176777; EP 436382; U.S. Pat. No. 3,721,644; U.S. Pat. No. 3,766,132; U.S. Pat. No. 3,770,811; U.S. Pat. No. 4,150,485; U.S. Pat. No. 4,514,174; U.S. Pat. No. 5,318,999; and Lee, H. L., et al (Aust. Dent. J., 22(4), 1977, 232-5). None of these citations, however, describe the specific materials of the present invention nor do they describe the rheology requirements to construct a dental compostion with superior handling capabilities.